1. Field
This invention relates to defect inspection of tubular elements, and more particularly to displaying the results of such defect inspection in a readily usable format.
2. Description of the Prior Art
Continuous tubular strings formed of connectable tubular sections or elements, such as production tubing strings, drill pipe strings and casing strings, are used in the drilling, completion and production of subterranean oil and gas wells. The individual tubular elements, which are typically steel castings, frequently contain manufacturing defects such as seams, laps, inclusions, and gouges which could result in costly failures if undetected prior to installation. Therefore, tubular elements are commonly inspected at the point of manufacture so that any serious defect can be located and repaired, if possible, before the defective tubing is shipped to the well site.
Tubular elements are also subject to various forms of mechanical damage after being installed within a well. It is therefore advantageous that the individual tubular elements comprising a tubular string be inspected periodically. Typically, the inspection of tubular sections occurs after the individual sections comprising the tubing string have been removed from the well and disengaged. Defect inspections are conventionally performed on a section by section basis.
A number of techniques exist for determining the presence of a defect in a tubing section. For example, the location of internal and external radially extending and three-dimensional defects, including slug inclusions, mechanical damage, pitting and fatigue cracks, has been determined by flux leakage techniques in which a longitudinal magnetic field is induced by one or more magnetic induction coils. External flux detectors are located around the tubing and the maximum signal is recorded to locate the defect. Similarly, longitudinal defects may be detected magnetically by the "rotating pole" method, where the magnetic field is applied from the outside by rotating electromagnets, and flux detectors positioned between the poles scan the outside surface of the pipe. Various techniques relating to electromagnetic inspection are well known in the art with a list of examples being set forth in the following patents:
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While electromagnetic inspection systems have become widely accepted in the industry, various other techniques are also available and may even be preferable depending on the circumstances. Such other inspection techniques include radiation as set forth in U.S. Pat. Nos. 3,835,323 and 3,855,465. Also but less frequently utilized, are ultrasonic inspection systems.
Any of the above mentioned inspection techniques may be utilized to adequately detect the presence of defects located within the wall of tubular elements. The most essential function of existing inspection devices is to generate an electrical signal containing information regarding physical characteristics such as defects and other irregularities in a given segment of a tubular member, and to display such information in a useful manner. Typically, the display consists of a strip chart generated on a strip recorder, indicating the aforementioned electrical signal in analog form with a graphic indication for each irregularity sensed by the detecting device. An inspection crew then utilizes the graph as a guide to visually confirm the existence of serious defects which would result in the rejection of the tubular element being inspected. Conventional graphic displays, however, are severely limited in their ability to convey useful information to the inspection crew responsible for visually locating defects.
A conventional strip chart display provides a very general indication of the existence of a defect and its longitudinal position along the length of a tubular member. The existence of a defect is indicated by one or more vertical peaks in the graph, while the longitudinal position roughly corresponds to the location of the peak (or peaks) along the horizontal axis. If the display contains a plurality of closely adjacent peaks, conventional systems do not distinguish between several closely adjacent defects, a single large defect, or several defects at the same longitudinal position but spaced apart circumferentially. In fact, with respect to the third situation, conventional systems provide virtually no useful information to the inspection crew regarding the circumferential location of any defects. In short, conventional displays provide no usable information regarding the shape, size or amplitude of a defect, and only minimal information regarding the location.
The absence of circumferential position indications in conventional graphic displays becomes an even greater problem when the tubing to be inspected contains a longitudinal weld seam. Since a seam is essentially a continuous irregularity extending from one end of the pipe section to the other, it appears on a conventional graphic display as a continuous string of defects indicated by a solid line of peaks. As such, the weld seam indications on the graphic display completely overshadow all other indications, thus making it virtually impossible to distinguish the weld seam from the defects.
In addition to the imprecise defect locating capabilities of prior art systems, conventional inspection devices typically employ band pass filters to remove extraneous information, such as the presence of certain non-defect irregularities, from the incoming signal. This technique is effective for the intended purpose, but the information filtered out is permanently lost. Conventional systems do not allow the user thereof to include all extreme signal values in the display, if so desired.